1. Field of the Invention
The present invention relates to an ink jet recording material and a process for producing the ink jet recording material and more particularly to an ink jet recording material having an gloss, a high excellent ink absorption and an excellent moisture and water resistibility.
2. Description of the Related Art
In an ink jet recording process, ink droplets which are injected through a nozzle at a high speed are attached to a recording material to effect recording. This type of recording is advantageous in that it can easily operate with a full color system and gives a low printing noise. The ink to be used in this recording process has a large content of a solvent. In order to obtain a high recording density, it is necessary to use a large amount of an ink. Further, since ink droplets are continuously injected, an ink droplet is injected before the preceding droplet is absorbed by the recording material, causing these ink droplets to be fused to each other to give fused ink dots. Accordingly, the ink jet recording material must have a high ink absorption volume as well as a high ink absorption rate.
Referring to the ink jet recording material of coated paper type, there is provided a porous pigment as a recording layer. In this arrangement, the color and sharpness governing the image quality are controlled to enhance the color reproducibility or image reproducibility. In order to cope with the rapid spread of ink jet printers, printed matters having a gloss as high as photograph are called for in uses such as publication and wrapping in the art of printing. In particular, in the case of color recording, from the standpoint of dot shape, dot sharpness, ink absorption, fixing rate and ink absorption volume, a film having a recording layer or a coated paper type of recording material is in great demand.
If the foregoing porous pigment is used, the pores formed by the pigment must be large because it is necessary that the ink be absorbed by the recording material. Accordingly, the pigment particles must be large. However, if the pigment particles are large, the desired surface smoothness of the recording layer cannot be obtained. Further, the light transmission is hindered, rendering the recording layer opaque. As a result, a high gloss cannot be obtained.
In general, in order to obtain an ink jet recording material having a high gloss, it is necessary that the transparency and smoothness of the recording layer be raised.
Referring to a support having a water-impermeable layer such as film and laminated paper, there is an attempt to obtain an ink jet recording material having a high gloss by the method described below or the like. For example, a system has been proposed in which a porous recording layer is formed on a transparent support such that an image formed on the recording layer can be observed from the support side (as disclosed in JP-A-61-197285 (The term "JP-A" as used herein means an "Unexamined Japanese Patent Publication (kokai)")). However, such a system is disadvantageous in that image processing must be effected such that mirror image is printed. Further, such a system is disadvantageous in that the support to be used is limited to a transparent material. Further, ink jet recording materials including a transparent and glossy support coated with a transparent resin which absorbs an ink upon dissolution and swelling are commercially available. However, these ink jet recording materials which absorb an ink by the dissolution and swelling of such a resin are disadvantageous in that it has a low ink drying rate and a high hydrophilicity and thus can be easily dissolved in water and exhibits a poor water resistance.
A recording material has recently been proposed comprising two or more layers wherein the upper layer is a gloss-developing layer. For example, in JP-A-7-101142, the preparation of an ink jet recording material having a high gloss is attempted by the lamination of a gloss-developing layer containing a pigment having an average particle diameter of not more than 300 nm dispersed therein as a main component. However, this proposal is disadvantageous in that the gloss-developing layer can easily sink in the recording layer. Thus, even if the surface of the recording material is smoothened by calendering, a highly smooth surface cannot be obtained due to the effect of roughness given by the pigment in the recording layer besides the surface roughness developed by coating. Further, an excellent gloss cannot be obtained. Further, in this application, in order to obtain a desired ink absorption rate, a high molecular latex is used as an adhesive (binder) to be incorporated in the gloss-developing layer. As a result, the coating layer is cracked, and the cracks thus obtained provides some ink absorption rate. However, the resulting ink dot has a notched circumference. Thus, the dot is far from circular. Further, dots are fused to each other, making it impossible to provide prints having a high fineness.
A process for the preparation of an ink jet recording material which comprises enhancement of surface smoothness, i.e., pressing the recording layer against a heated mirror-like roll while a gloss-developing layer containing a colloidal silica or colloidal silica composite incorporated therein as a main component is wet, and then drying the material is proposed (JP-A-7-117335). This process is known as a process for allowing a film-forming substance such as adhesive to trace the surface of the mirror-like drum in the cast coater as disclosed in U.S. Pat. No. 5,272,846.
The cast-coated paper obtained according to the foregoing process is disadvantageous in that the resulting coating layer loses porosity due to the presence of the film-forming substance and hence exhibits a reduced ink absorption during ink jet recording. In JP-A-7-117335, as the adhesive there is used a high molecular latex. In this arrangement, the coating layer undergoes drastic cracking on the order of micron meter to have ink absorption. However, since the gloss-developing layer can be cracked similarly to the above mentioned case, prints having a high fineness cannot be obtained. Further, since it is necessary that water vapor or the like pass through the coating layer and paper during drying, pinholes can be easily formed, making it impossible to obtain an ink jet recording material having excellent gloss, smoothness and luster as high as photograph.
Further, since the casted paper is inherently pressed against the cast drum during drying, the coated paper must have an air permeability (to allow the passage of water vapor during drying). In other words, a film-based (including laminated paper) cast-coated sheet is difficult to be prepared.
In addition, various methods have been attempted to obtain an ink jet recording material having a high gloss. Examples of these attempts include a process which comprises laminating the recorded surface after ink jet recording to attain a high gloss as disclosed in JP-A-61-230973, JP-A-61-230974, JP-A-61-230975, and JP-A-61-230976. However, lamination after printing has a problem of mechanical facility and high cost and thus cannot be normally applied.
Further, as disclosed in JP-A-63-151476, a process is proposed for obtaining an ink jet recording sheet having a desired surface which comprises applying a coating mainly composed of a pigment and a binder to a support to form a coating layer, semi-drying the coating layer, superposing a transferring sheet having a desired surface condition (including high surface smoothness) on the surface of the coating layer, drying the laminate, and then peeling the transferring sheet off the surface of the coating layer to obtain a characteristic surface condition (including high surface smoothness). However, in this transferring process, a film or a transferring sheet having a desired surface condition is pressed against a coating layer which is in semi-dried state. Thus, the control over the drying condition is extremely difficult. Further, when the transferring sheet is laminated on the coating layer, air bubbles or the like can be easily contained in the coating layer, making it impossible to obtain a high smoothness. In this process, lamination is effected during drying similarly to casting method. Thus, the support and/or transferring sheet must be permeable to air. However, pinholes can be easily formed in the coating layer similarly to casted paper. Accordingly, an ink jet recording material having a gloss and smoothness as high as photograph can hardly be obtained.
Referring to an ink jet recording material having a high gloss, a system is proposed in which an image formed on a porous recording layer formed on a transparent support is observed from the support side (JP-A-61-197285). However, such a system is disadvantageous in that image processing must be effected such that mirror image is printed. Further, such a system is disadvantageous in that the support to be used is limited to a transparent material.
On the other hand, in order to control the color and sharpness governing image quality in the coated paper type of recording material, a recording layer (consisting of a single layer or a plurality of layers) containing a porous pigment incorporated therein is provided in an attempt to enhance the color reproducibility or image reproducibility. For example, as disclosed in JP-A-63-13776 and JP-A-63-104878, an ink jet recording material is proposed having a recording layer containing primary or secondary porous particles as pigment particles and a binder incorporated therein.
Further, a process is proposed for providing an ink jet recording material having a higher image quality which comprises forming pores in the uppermost layer of the recording layer in such an arrangement that pore diameters have peaks in the range of from 0.2 to 10 .mu.m to raise the ink absorption rate, whereby an ink absorbed by the recording layer is taken in by voids having a pore diameter of not more than 0.05 .mu.m, for the purpose of enhancing the print quality, as disclosed in JP-B-63-22997 (The term "JP-B" as used herein means an "examined Japanese patent publication"). It is necessary that the size of pigment particles themselves or secondary particles be raised to render the foregoing layer porous. However, if the size of pigment particles is increased, the surface of the recording layer cannot be provided with smoothness. Further, the light transmission is hindered, rendering the recording layer opaque. Thus, a color recording having a high gloss which is as beautiful as photograph cannot be obtained.
As ink jet recording materials having a pigment-containing layer there have been reported many ink jet recording papers having a recording layer formed by a pigment such as silica, alumina, pseudo-boehmite, calcium carbonate and kaolin and a water-soluble high molecular compound such as starch and polyvinyl alcohol cellulose derivative as an adhesive. Such a recording layer has an excellent water resistance but normally has no smoothness and gloss. For example, as disclosed in JP-B-61-60793 and JP-A-2-274587, a synthetic silica, a colloidal silica, and a water-soluble high molecular adhesive are used to form such a recording layer. However, in order to keep the desired ink absorption, the incorporation of a synthetic silica having a relatively large particle diameter is indispensable. A synthetic silica normally has a large particle diameter. Thus, the desired smoothness and gloss can hardly be obtained.
Further, in order to provide a recording layer on various substrates, EP-0648611A1 discloses an ink jet recording material obtained by a process which comprises forming a recording layer on a release material, forming an adhesive layer on the recording layer, laminating the obtained material on various substrates, and then peeling a release material off the laminate to obtain a laminate of recording layer, adhesive layer and substrate. In this case where an adhesive layer is provided on a recording layer, in the case where the recording layer contains a pigment and thus absorbs an ink by the porosity, when an adhesive layer is applied to the recording layer, the adhesive penetrates through the pores, causing the drastic reduction of ink absorption rate of the recording layer. Further, since the recording layer is porous, numeral air bubbles are formed in the adhesive layer, eliminating the smoothness of the recording layer and hence impairing the external appearance. If the recording layer is not porous, an ink is absorbed by the swelling of the recording layer. Thus, the ink absorption rate is reduced. Further, the surface smoothness is eliminated by swelling. Moreover, since the resulting coat layer has no water resistance, a satisfactory ink jet recording material cannot be obtained.